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Does Insulin Resistance Contribute to Worse Breast Cancer Prognosis in Black Women?

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A study suggests that insulin resistance may be part of the reason why black women have worse breast cancer prognoses than white women.

The research was published on May 12, 2020, by the journal Breast Cancer Research. Read “Insulin resistance contributes to racial disparities in breast cancer prognosis in US women.”

Breast cancer in black and other minority women

Research has shown that black women are more likely than any other ethnic group to die from breast cancer. Black women also:

  • are more likely to be diagnosed with triple-negative breast cancer, which means the cancer has no receptors for the hormones estrogen and progesterone, as well as no receptors for the HER2 protein; this limits the medicines that can be used to treat the cancer
  • are more likely to be diagnosed with later-stage disease than other women
  • have the lowest survival rates in each stage of diagnosis

Experts have suggested that these racial disparities in breast cancer diagnoses and outcomes are likely due to a combination of factors. Research suggests that the biology of breast cancer is different in black women. Rising obesity rates among black women, coupled with statistics showing that more black women are having fewer children and having children later in life, could play a role. We also know that black women are less likely to participate in clinical trials testing new breast cancer treatments. Some doctors think that it’s possible that some medicines work differently or less effectively in black women.

Insulin resistance

Insulin is a hormone that’s made in the pancreas and works throughout the body. Its job is to regulate your blood sugar (glucose) levels and to control the amount of energy that you put into and take out of your fat stores. Insulin resistance means your cells stop responding to insulin the way they should.

Because your cells aren’t responding to insulin, your pancreas thinks the body doesn’t have enough insulin and produces more. Over time, this makes your blood sugar levels go up. High blood sugar can lead to weight gain, diabetes, heart disease, and high blood pressure and is linked to a higher risk of developing several different types of cancer.

Together, insulin resistance, high blood pressure, a large amount of abdominal fat, and high triglycerides/cholesterol levels are called metabolic syndrome. Metabolic syndrome is linked to a higher risk of breast cancer, as well as a worse prognosis if breast cancer is diagnosed.

According to statistics from the U.S. government, black women are 20% more likely to have metabolic syndrome than white women.

In the study reviewed here, the researchers wanted to know if insulin resistance was part of the reason why black women have worse breast cancer prognoses than white women.

How the study was done

The study included 515 women who lived in New York, New Jersey, Connecticut, Maryland, and Michigan who were diagnosed with early-stage breast cancer:

  • 83% were white
  • 17% were black
  • average age was 58.3
  • 97% of white women were diagnosed with stage I or stage II disease
  • 94% of black women were diagnosed with stage I or stage II disease

Women who had been diagnosed with diabetes were not allowed to participate in the study.

The researchers looked at the women’s medical records and also weighed, measured, and took fasting blood samples from them.

Overall, 24% of the women were considered obese, 72% were considered to have large amounts of abdominal fat, 11% were insulin resistant, and 23% had metabolic syndrome. But when the researchers looked at these risk factors by race, black women were more likely to have these conditions:

  • 19% of white women were considered obese compared to 47% of black women
  • 67% of white women had large amounts of abdominal fat compared to 96% of black women
  • 20% of white women had metabolic syndrome compared to 40% of black women
  • 10% of white women were insulin resistant compared to 17% of black women

Compared to white women, black women were more likely to have worse breast cancer prognoses. When the researchers adjusted the formula they used to figure out the women’s prognoses to include differences in insulin resistance, they found that the prognoses of black and white women were similar.

“At the beginning of the study, we hypothesized that insulin resistance was a factor contributing to the racial disparities in breast cancer prognosis, so the results were in keeping with our hypothesis," said lead author Emily Gallagher, M.D., of Mount Sinai, in an interview. "As an endocrinologist, I think it is important to recognize that insulin resistance is not just a risk factor for cardiovascular disease and diabetes, but is also a risk factor for certain cancers.

"In our study, we see that insulin resistance is a factor that contributes to the racial disparities in prognosis that exist in women with newly diagnosed breast cancer," she continued. "We next need to understand if reducing insulin resistance will narrow the racial disparities in the risk of developing poor prognosis breast cancer.”

What this means for you

You can’t tell if you have insulin resistance by the way you feel, and testing for insulin resistance isn’t routinely done in doctors’ offices. Still, it’s likely that you’re at higher risk for, or may have, insulin resistance if you have a:

  • waist measurement of more than 35 inches if you’re a woman and more than 40 inches if you’re a man
  • blood pressure reading of 130/80 or higher
  • fasting blood sugar level of more than 100 mg/dl
  • fasting triglyceride level of more than 150 mg/dl

If you think you have insulin resistance or are at high risk for the condition, it makes sense to talk to your doctor about it and come up with a plan to reduce your risk and help reverse the condition if you do have it:

  • Exercise makes you more sensitive to insulin and can also help you lose weight. The American College of Sports Medicine recommends that people who have been treated for cancer do moderate-intensity aerobic exercise 3 times per week for at least 30 minutes and do resistance exercise at least 2 times per week.
  • Eat a healthy, varied diet that’s low in processed foods and high in fresh foods with lots of fiber.
  • Get enough sleep to help your body recover and reduce stress.

For more information, visit the Breastcancer.org pages on Exercise and Nutrition. You also may want to check out this Think Pink Live Green column on insulin resistance by Marisa Weiss, M.D., Breastcancer.org founder and chief medical officer.

Written by: Jamie DePolo, senior editor

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